You look at the figures and you think: 'That's impossible.' Uganda had about 7 million people at independence in 1962, and in only 45 years it has grown to 30 million. By 2050, just over four more decades, there will be 130 million Ugandans, and it will be the 12th biggest country in the world, with more people than Russia or Japan. Its population will have increased 18-fold in less than 90 years.
Many people think that population growth is no longer a problem, and everybody somehow knows that it is politically incorrect to talk about it. Back in 1968, when Paul Ehrlich terrified everybody with his book The Population Bomb, it was seen as the gravest long-term threat facing the human race. But now it scarcely gets a mention, even in discussions on climate change - as if the number of people producing and consuming on this planet was irrelevant to the pressure on the environment.
True, the population explosion has gone away in large parts of the world, in the sense that most developed countries now have birth rates well below replacement level (2.1 children per woman): the global average, including the developing countries of Asia and South America, is now down to 2.3 children. That's pretty impressive, given that it was 5.4 children per woman as recently as 1970. But there remains the problem of what you might call 'inertial growth'.
My own mother had five children, which was not seen as at all unusual at the time. In the next generation of our family, by contrast, the birth rate has dropped to 2.0: we five brothers and sisters and our five spouses have had a total of just 10 children. But that doesn't mean that our population boom stopped.
It would have if we had just spawned and died, but we insisted upon living on after our children were born. In fact, we're all still here, although the first grandchildren are already starting to appear - so where there were once 10 of us, there are now 23. It takes two full generations at replacement level before the population finally stabilises.
That process accounts for about half of the anticipated population growth in the next 40 years, which will raise the total number of people on the planet from 6.5 billion to about 9 billion. But the other half of the growth comes mainly from Africa, already the poorest continent.
This may explain why it became politically incorrect to talk about population growth around 25 years ago. Nine of the 10 countries with the highest birth rates are African (the other is Afghanistan), and it seemed uncomfortably like pointing the finger at the victim. But runaway population growth is a big factor in making so many Africans victims, and it doesn't help to stay silent about it.
Sometimes the steadily worsening ratio of people to resources just causes deepening poverty, as in Nigeria, whose population by 2050 will reach 300 million. That is the same as the current population of the United States, but Nigeria, apart from being virtually without industry, does not have one-tenth of the natural resources of the US. If those 300 million people live at all, they will live very badly.
Often, however, the growing pressure of people on the land leads indirectly to catastrophic wars: Sierra Leone, Liberia, Uganda, Somalia, Congo, Angola and Burundi have all been devastated by chronic, many-sided civil wars, and all seven appear on the top-10 birth-rate list. Rwanda, Ethiopia and Mozambique, which have suffered similar ordeals, are just out of the top 10.
Africa, which accounted for only 8 per cent of the world's population in the 1960s, will contain almost a quarter of the world's (much larger) population in 2050.
Uganda's birth rate is seven children per woman, little changed from 30 years ago. Uganda's president, Yoweri Museveni, believes that his country is underpopulated, and told parliament last July: 'I am not one of those worried about the population explosion. It is a great resource.' He has done many good things for his country, but this one blind spot could undo them all. And he is far from alone.
Gwynne Dyer is a London-based independent journalist whose articles are published in 45 countries